The proposed research is focused on the details of excimer laser light interaction with coronary artery tissue in the presence of a fluid medium. The purpose of the research is to understand how photoablation is accomplished in a diseased artery by pulsed excimer radiation through an optical fiber surrounded by a fluid field. Such information is essential for the optimization and control of laser light energy in a percutaneous laser angoiplasty procedure. The mechanism of excimer laser action will be determined by a full range of photophysical and photochemical measurements on coronary artery segments. The measurements will be made with excimer wavelengths which have been shown by our previous work to be efficiently transmitted through optical fibers (351 nm) and capable of effecting tissue photoablation in the presence of saline, Fluosol and blood. These measurements will include: 1. determination of the photoablation threshold for coronary segments under fluid 2. determination of extent of formation of particulate matter released in fluid media 3. analysis of photoproducts released in both gas and liquid phase 4. analysis of photoemission accompanying photoablation 5. determination of extent of free radical formation on photoablation by spin trapping 6. determination of spread of laser energy by photoacoustic spectroscopy The proposed research program will bring the full power of spectroscopic and modern analytical measurements to the determination of the detailed understanding of the excimer photoablation process in coronary atherosclerotic lesions. Unlike several previous studies of excimer interactions with cardiovascular tissue, including those from our own laboratory, the determination of photophysical mechanisms active will be accomplished in the presence of three important fluid fields - blood, saline and the blood-substitute, Fluosol. Such experiments are expected to be of central importance to the determination of the optimum laser parameters required for the controlled use of excimer laser light energy in percutaneous laser angioplasty.